Overland flow, erosion, and related phosphorus and iron fluxes at plot scale: a case study from a non-vegetated lignite mining dump in Lusatia

Long-term high resolution measurements of precipitation, soil water budget, surface runoff, and sediment transport as well as rainfall simulations at plot scale have been accomplished on a non-vegetated lignite mining dump (Germany, Lusatia, Schlabendorf-North), completed by measurements of infiltration and water drop penetration time. The investigations revealed that the distribution of hydraulic properties is mainly related to ridges, rills, and gullies, structuring the dumps. Soil moisture time series on a ridge showed nearly no response to rainfall events. Infiltration measurements and rainfall simulations indicate, that the ridges bare of vegetation predominantly have a very low infiltration capacity, which is caused by water repellency. Even low rainfall intensities generate surface runoff. In contrast, gullies show no hydrophobic properties but high infiltration capacities, although the tipped sediment is identical in texture. Surface runoff and erosion may only be explained by the spatial pattern of ridges, gullies, and rills. The current P loss from those non-vegetated sites is very low due to low P contents in eroded matter. Since the very low P fluxes and the very low portions of water-extractable P are accompanied by higher Fe portions, which result in Fe/P ratios of up to 130, the P losses are not relevant for a eutrophication of the adjacent acid mining lakes. Hence, this study aims to the estimation of the runoff and erosion processes and the related P and Fe fluxes at plot scale, as a contribution to the development of the post mining landscape at the interface of soil and surface water.